Engine turbocompressor controllable bypass system and method

ABSTRACT

A system for a turbocharged internal combustion engine includes an engine having a charge inlet connected to the compressor outlet and an exhaust outlet connected to the turbine inlet for driving the turbocharger with hot exhaust gas and supplying compressed air to the engine for combustion. A bypass duct connects the compressor outlet to the turbine inlet for diverting a portion of the compressed air around the engine to the turbine inlet. A control member selectively controls the diversion of air. An operating method for the system involves controlling surge in an engine turbocharger compressor by diverting a portion of compressed air to the turbine inlet to limit compressor air pressure and insure sufficient air flow to avoid compressor surge. Preferably, the diverted air enters a distal part of an engine exhaust header for mixing with the exhaust gases prior to passing into the turbine inlet. Other benefits are disclosed.

TECHNICAL FIELD

[0001] This invention relates to turbocharged internal combustionengines, such as diesel engines, and more particularly to a system andmethod for controlling compressor surge in the turbocharger andproviding certain operational and performance advantages.

BACKGROUND OF THE INVENTION

[0002] It is known in the art to utilize a wastegate in connection witha turbocharger compressor to bypass some of the compressor outlet airdirectly to the exhaust outlet of the turbocharger. The wastegate isopened when necessary to avoid compressor surge by increasing air flowthrough the compressor while reducing the pressure differential acrossthe compressor. The bypass action of the wastegate also reduces air flowthrough the engine and therefore the cylinder charge. This has theeffect of reducing peak combustion pressures and temperature resultingin reduced emissions of nitrogen oxides (NOx). The thermal load on thecharge air cooler, or aftercooler, is also reduced by reducing theengine air flow by means of the wastegate. However, the bypassed air isnot utilized and thus creates an energy loss in the system.

[0003] There are turbocharged diesel engine operating conditions whichproduce a higher cylinder trapped oxygen content than is required forefficient combustion. Typically, this results in higher NOx productionbecause of the resulting higher peak pressure in the cylinders andincreased oxygen available to combine with free nitrogen. A system andmethod for controlling compressor surge and further lowering controlledengine exhaust emissions is desired.

SUMMARY OF THE INVENTION

[0004] The present invention involves taking a portion of the compressordischarge air and bypassing the charge air cooler and engine cylindersand re-injecting the compressed air prior to the turbine inlet. Thebypassed air is preferably directed through the engine exhaust header ormanifold, if provided. The bypass duct around the charge cooler andengine is provided with a control valve to limit air flow through thebypass to a desired value. The valve may be operated by suitablecontrols responsive, for example, to turbocharger compressor air flowand/or differential pressure and rotor speed to determine the propersetting of the bypass control valve.

[0005] The novel bypass system may be utilized under various engineoperating conditions to prevent surge of the turbocharger compressor byincreasing air flow and/or reducing differential pressure. Where theengine air charge pressure is greater than needed, the opening of thesurge control bypass will result in reduced cylinder pressure as well asreduced cylinder oxygen content, both of which will result in theproduction of lower NOx emissions. The bypass of compressor air directlyinto the engine exhaust manifold will reduce manifold exhausttemperature and lower the NOx produced in the exhaust. It will alsoimprove turbine life by reducing maximum turbine temperatures. Thesystem additionally recovers a large percentage of the compressordischarge energy by passing the compressed air through the turbine.Further, the bypassed air provides additional oxygen to the exhaustwhich helps burn up any excess hydrocarbons. Additionally, the reducedair flow through the engine also reduces the cooling load on theaftercooler, providing for more efficient system operation.

[0006] These and other features and advantages of the invention will bemore fully understood from the following description of certain specificembodiments of the invention taken together with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The single FIGURE of the drawing is a schematic side view of anengine including a turbocharger and a system for controlling compressorsurge in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0008] Referring now to the drawing in detail, numeral 10 generallyindicates an internal combustion engine assembly, such as a dieselengine for railroad locomotives, marine applications and other uses.Assembly 10 includes an engine 12 having a charge air inlet 14 and anexhaust outlet including an engine exhaust manifold 16. A turbocharger18 is mounted on or adjacent to the engine and includes internally aturbine 20 driving a compressor 22.

[0009] The compressor includes an ambient air inlet 24 and a compressedair outlet 26. The turbine includes an exhaust gas inlet 28 and anexhaust discharge or outlet 30.

[0010] The compressor outlet 26 is conventionally connected through aduct 32 with an inlet header 34 for a charge air cooler 36. The aircooler 36 discharges to a manifold or header 38 which delivers cooledcompressed inlet air to the engine cylinders, not shown. The enginecylinders discharge through one or more exhaust outlets 40 to theexhaust manifold 16, which carries the engine exhaust gas to the inlet28 of the turbine for driving the turbocharger. The spent exhaust gas isdischarged through the turbine exhaust 30.

[0011] In accordance with the invention, the engine assembly 10 includesand forms a part of a surge control system 42 for controlling surge inthe turbocharger compressor as well as for providing other benefits. Inaddition to the elements described above, the surge control system 42includes a bypass duct 44 which connects the charge air cooler inletheader 34 directly with the engine exhaust manifold 16 at an end 46distal from the turbine exhaust gas inlet 28. The bypass duct 44 hasmounted therein a bypass control valve 48 which may be operated in anysuitable manner, such as by an electronic or electro-mechanical control50. Control 50 may be actuated through suitable sensors, not shown, inresponse to operational data such as pressure differential, air flowand/or compressor speed. Operating conditions can be programmed tomaintain the compressor in a surge-free operational condition.

[0012] In operation of the engine, especially at higher load conditions,the turbocharger speed may provide greater air pressure and flow than isneeded in order to properly burn the fuel supplied to the engine. Undersome conditions, the exhaust back pressure may increase excessively,limiting air flow through the compressor and approaching a condition ofsurge. Under such circumstances, sensed conditions within theturbocharger will actuate the control 50 to open the bypass valve 48 acontrolled amount. This will allow some of the compressor discharge airto be bypassed around the charge cooler 36 and engine cylinders, notshown, directly to the engine exhaust manifold 16 at the end 46 distalfrom the turbine inlet 28. Bypassing of the charge cooler and engineimmediately increases turbocharger airflow and reduces the differentialpressure, so as to avoid compressor surge. Air flow through the chargeair cooler and engine cylinders is also reduced so that the thermal loadon the charge cooler is lowered. Also, air trapped in the enginecylinders is reduced so that oxides of nitrogen production in thecylinders is lowered because of the reduced temperatures and excess airpresent. At the same time, the air bypassed through the bypass duct 44passes through the exhaust manifold 16 where it mixes with the engineexhaust gases, and its oxygen content assists in burning up excesshydrocarbons in the exhaust. Additionally, the energy of the bypassedcompressor air adds to the exhaust energy upon entering the turbine 20of the turbocharger so that the energy is used in maintaining theturbocharger speed prior to discharging to atmosphere with the otherexhaust gases through the turbine exhaust discharge 30. The reduction incylinder pressure in the engine because of the lower exhaust chargesalso helps reduce NOx formed during combustion in the cylinders.

[0013] Considered as a method, the present invention involvescontrolling surge in an engine turbocharger compressor by diverting asufficient portion of the compressed air from the compressor outletaround the engine to the turbine inlet to limit compressor air pressureand insure sufficient airflow to avoid compressor air surge conditions.The method may also include passing the diverted air through the engineexhaust header or manifold for mixing with the exhaust gases prior topassing into the turbine inlet. Excess oxygen in the diverted air isthen available for burning hydrocarbons present in the engine exhaustmanifold. The method may also include operating the control valve in thebypass duct to reduce engine cylinder pressures and temperatures. It canalso control air flow thorough the charge air cooler to obtainreductions in engine created NOx and to lower the cooling load in thecharge air cooler where such operation may prove of benefit inconserving energy or controlling emissions.

[0014] While the invention has been described by reference to certainpreferred embodiments, it should be understood that numerous changescould be made within the spirit and scope of the inventive conceptsdescribed. Accordingly, it is intended that the invention not be limitedto the disclosed embodiments, but that it have the full scope permittedby the language of the following claims.

1. A controllable bypass system for a turbocharged internal combustionengine, the system comprising: an engine having a charge inlet and anexhaust outlet; a turbocharger including a turbine driving a compressor,a turbine inlet connected to the engine exhaust outlet for driving theturbine with hot exhaust gas and a compressor outlet connected to theengine charge inlet for supplying compressed air to the engine forcombustion; a bypass duct connecting the compressor outlet to theturbine inlet for diverting a portion of the compressed air around theengine from the compressor outlet to the turbine inlet; and a controlmember for selectively controlling the diversion of air through thebypass duct.
 2. A system as in claim 1 wherein the control member is acontrol valve in the duct and is externally operable for controllingbypass air flow.
 3. A system as in claim 2 wherein the control valve isoperated by a controller responsive to air flow and pressuredifferential across the compressor to provide bypass air flow asrequired to avoid surge in the compressor air flow.
 4. A system as inclaim 1 including a charge air cooler in the engine charge inlet forcooling the compressed air prior to combustion in the engine.
 5. Asystem as in claim 1 wherein the engine includes an exhaust manifoldforming part of the engine exhaust outlet and the bypass duct isconnected to the exhaust manifold at an end distal from the turbineinlet
 6. A method of controlling surge in an engine turbochargercompressor, the method comprising: diverting a sufficient portion of thecompressed air from the compressor outlet around the engine to theturbine inlet to limit compressor air pressure and insure sufficient airflow to avoid compressor surge conditions while utilizing the energy inthe diverted air to maintain compressor speed.
 7. A method as in claim 6including passing the diverted air through an engine exhaust header formixing with the exhaust gases prior to passing into the turbine inlet.8. A method of controlling NOx production in an engine having aturbocharger, the method comprising: diverting a controlled portion ofcompressed air from the compressor outlet around the engine to theturbine inlet to limit oxygen content in the cylinders and therebyreduce NOx production in the cylinders while utilizing the energy in thediverted air to maintain compressor speed.
 9. A method as in claim 8including passing the diverted air through an engine exhaust header formixing with the exhaust gases prior to passing into the turbine inlet.10. A method of controlling peak cylinder pressure in an engine having aturbocharger, the method comprising: diverting a portion of thecompressed air from the compressor outlet around the engine to theturbine inlet to limit oxygen content in the cylinders and reduce thecombustion rate, thereby limiting peak pressures in the engine cylinderswhile utilizing the energy in the diverted air to maintain compressorspeed.
 11. A method as in claim 10 including passing the diverted airthrough an engine exhaust header for mixing with the exhaust gases priorto passing into the turbine inlet.